Interfering absorption from background gases in a gas stream may limit detection sensitivity or even prevent detection of trace gas contaminants for absorption spectroscopy-based gas sensing systems. Among other potential problems, an inability to sensitively detect critical trace gas contaminants can present risks of serious human health and environmental hazards; damage to machinery; increased production costs; and/or degradation of product quality and product value in industrial, chemical, medical, pharmacological, and energy applications. For example, for moisture detection in natural gas (NG), it can be difficult to find a water vapor absorption transition which is totally free of background absorption interference from methane (CH4), the predominant background gas in the NG stream.